What sort of criterion is it to use resource size to judge the...

What sort of criterion is it to use resource size to judge the biggest mine in the world??

Its not the size of the resource but what you do with it. (as my missus would say)

Grotegeluk (EXXARO , Waterberg) is generally acknowledged as one of the biggest producing coal mines in the world at close to 40 mtpa, and they have the reserves to go with it.
Vale in mocambique are planning to produce 50 Mtpa ROM at Vale which will make it THE biggest. These are the yardsticks to measure against.